It is known that for practising winter sports, like Alpine skiing, both as a competitive and professional activity and as a leisure time activity, a particular type of boot must be worn.
This boot comprises a shaped shell currently made, in most cases, of a plastic material, that develops mainly along a horizontal longitudinal axis, but for a short section also along another substantially vertical longitudinal axis.
The shaped shell is provided with a flat sole that, especially at the level of the heel and toe, is shaped in such a way as to adapt to the ski bindings.
The shaped shell is also equipped with a pair of buckles, used to close the boot tightly once the user has put it on, applied to the area of the outer surface that rests against the top of the foot.
In some known models, the boot comprises also a leg, associated with the shaped shell by means of pins, which surrounds and protects part of the user's leg.
A specific type of boots currently available on the market offers the possibility to vary the length of the shaped shell and has been designed especially for children or young persons that are still growing up, as well as for hire shoos that must be rather flexible as regards the available boot sizes.
In this regard, patents EP 1 428 443 and FR 2 358 117 are referred to as examples of prior art.
The boots with adjustable length of known type comprise a shaped shell that includes a rear portion, suited to surround at least the heel of the user's foot, and a front portion, known to anyone skilled in the art as “lower shell”, that develops mainly along a longitudinal axis.
The front portion is suitable for surrounding the distal region and the top of the foot and is telescopically associated with the rear portion, to which it is permanently connected through fixing means, usually screws.
The fixing means are inserted in threaded through holes, made coaxially in both the above mentioned portions starting from the lower surface, that is, the surface that is in contact with the ski or the ground, belonging to the rear portion.
Therefore, the front portion partially overlaps the rear portion, to which it is telescopically coupled.
The boot length can be varied with the aid of sliding means comprising projections that, depending on the case, are arranged on the upper surface of the rear portion or on the lower surface of the front portion.
These projections, for example pins, are slidingly arranged in corresponding grooves obtained on the lower surface of the front portion or on the upper surface of the rear portion, respectively.
In this way, according to the known art, to modify the length of the boot, which may be necessary, for example, due to the growth of the foot, the user loosens the fixing means, which locked the mutually sliding portions of the shaped shell in the previous position, partially extracts the front portion from the rear portion and locks them in the new position using the fixing means again.
However, the boots carried out according to the known art just described have some drawbacks.
The main drawback of the boots of known type lies in that the operation for adjusting the length of the shaped shell is rather complex and long to carry out. In fact, it often happens that the user has to repeat more than once the operations necessary to handle the fixing means and to modify the mutual position of the front and rear portions before achieving the optimal length of the shaped shell, suited to the size of the user's foot.
This is due to the fact that the sliding means allow the shaped shell to be adjusted only in a continuous way, that is, increasing or reducing its length by an indefinite and imprecise value.
Consequently, the user carries out the adjusting operations without the aid of any reference element, appreciatively, which inevitably prolongs the time required to achieve the desired length.
A further drawback derives from the fact that the connection between the front portion and the rear portion is not optimal and leaves a slack between them, due to the position in which the fixing means are generally applied.
Consequently, the conditions of use of the boot on the one hand are uncomfortable and troublesome for the user and on the other may also affect the soundness of the boot over time.